44 PROCEEDINGS OF THE AMERICAN ACADEMY 



plete halving of the cell, together with its contents; each of the halves 

 thus formed undergoes the same process of division, and so on to a 

 greater or less number of subdivisions, the products being, not seg- 

 ments of a sphere, as would be the case from the division of inorganic 

 matter, but miniature cells, resembling, in every particular except 

 mere size, the original cell. This spontaneous division and subdi- 

 vision of organic matter, by which definite particles reproduce their 

 kind, lies at the very foundation of the successive continuation of all 

 specific organized forms in the vegetable and animal world. 



" Until late years, this process of segmentation was supposed to 

 belong exclusively to the impregnated ovum, and to be the index of its 

 state of fecundation. Recent researches in histology, however, have 

 shown, not only that it is a very common phenomenon with most in- 

 dividual cells, but also that it may occur in the ovum before fecunda- 

 tion ; that is, is not the direct sequela of this last. In epithelial cells, 

 as also those belonging to various morbid growths, I have watched 

 this process occurring exactly as with the ovum ; and in the ova of the 

 common codfish {Gadus morrhiia), before expelled from the ovaries, 

 and therefore before impregnation, I have seen phenomena indicating 

 that the segmentation of the vitellus had already commenced. 



" But we will examine the details of this process as occurring 

 where they are mostly completely expressed, in the impregnated egg. 

 Throughout the entire organized world, the development of new indi- 

 vidual forms from the ovum which has its origin in a proper sexual 

 organ, is always preceded by this process, to a more or less complete 

 extent ; this segmentation may, indeed, go on to a certain extent be- 

 fore fecundation, as already remarked, but its continuance ending in 

 the evolution of a new individual form is invariably dependent upon 

 the act of fertilization by the male product, or sperm. I wish to insist 

 upon this point in reference to some remark soon to be made. It may 

 be said further, that not only is the whole individual formed out of the 

 segmentation products, but at those points of the animal which contain 

 tissues of the noblest function is always the most complete ; such, for 

 instance, is the case with the line of the nervous centres. 



" The sperm-cell being the analogue of the ovum, these same phe- 

 nomena, just described, are observed to precede the formation of the 

 spermatic particle, and I can confidently affirm that no spermatic 

 particle is produced without the occurrence of these preliminary 

 processes. 



